Fatal pitfalls in newborn screening for mitochondrial trifunctional protein (MTP)/long-chain 3-Hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency

Sudden Death of a Four-Day-Old Newborn Due to Mitochondrial Trifunctional Protein/Long-Chain 3-Hydroxyacyl-CoA Dehydrogenase Deficiencies and a Systematic Literature Review of Early Deaths of Neonates with Fatty Acid Oxidation Disorders

Mitochondrial trifunctional protein (MTP) and long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiencies have been a part of the Slovenian newborn screening (NBS) program since 2018. We describe a case of early lethal presentation of MTPD/LCHADD in a term newborn. The girl was born after an uneventful pregnancy and delivery, and she was discharged home at the age of 3 days, appearing well. At the age of 4 days, she was found without signs of life. Resuscitation was not successful. The NBS test performed using tandem mass spectrometry (MS/MS) showed a positive screen for MTPD/LCHADD. Genetic analysis performed on a dried blood spot (DBS) sample identified two heterozygous variants in the HADHA gene: a nucleotide duplication introducing a premature termination codon (p.Arg205Ter) and a nucleotide substitution (p.Glu510Gln). Post-mortem studies showed massive macro-vesicular fat accumulation in the liver and, to a smaller extent, in the heart, consistent with MTPD/LCHADD. A neonatal acute cardiac presentation resulting in demise was suspected. We conducted a systematic literature review of early neonatal deaths within 14 days postpartum attributed to confirmed fatty acid oxidation disorders (FAODs), which are estimated to account for 5% of sudden infant deaths. We discuss the pitfalls of the NBS for MTPD/LCHADD.

Circulatory response to exercise relative to oxygen uptake assessed in the follow-up of patients with fatty acid beta-oxidation disorders

Patients with fatty acid oxidation disorders (FAODs) experience muscle symptoms due to impaired ATP metabolism and the toxicity of accumulated mitochondrial FAO substrates or intermediates, especially during catabolic states. A major issue is the absence of specific and sensible biomarkers to evaluate metabolic equilibrium. The relationship between cardiac output (Q) and oxygen consumption (VO2) during incremental exercise (dQ/dVO2) provides an indirect surrogate of mitochondrial function. A high dQ/dVO2 slope indicates impaired oxidative phosphorylation in skeletal muscle during exercise. Our study aimed to evaluate dQ/dVO2 as a potential marker of the severity of FAODs. We retrospectively collected clinical, laboratory parameters and treatment data for FAOD patients over 6 years old, including a disease severity score, plasma acylcarnitines and cardiopulmonary exercise tests with Q measurement via thoracic bioelectrical impedance. FAO flux was measured in whole blood and in myoblasts when available. We included 27 FAOD patients followed from 2015 to 2022, with deficiencies in LCHAD (n = 10), CPT2 (n = 6), VLCAD (n = 7), or MADD (n = 4). CPT2 deficient patients with severe scores had the highest C18:1-, C16-, C18-acylcarnitines, and dQ/dVO2. In these patients, dQ/dVO2 was positively correlated with C18:1, C16, and C18 acylcarnitines. In a linear multivariate regression model, dQ/dVO2 was significantly associated with the severity score (B = 0.831, p = 0.008) and triheptanoin treatment (B = -0.547, p = 0.025). dQ/dVO2 and plasma long-chain acylcarnitines might be useful to monitor CPT2D, as these parameters associate with our clinical severity score and could reflect altered mitochondrial functions.

Syndromic Retinitis Pigmentosa

Retinitis pigmentosa (RP) is a progressive inherited retinal dystrophy, characterized by the degeneration of photoreceptors, presenting as a rod-cone dystrophy. Approximately 20-30% of patients with RP also exhibit extra-ocular manifestations in the context of a syndrome. This manuscript discusses the broad spectrum of syndromes associated with RP, pathogenic mechanisms, clinical manifestations, differential diagnoses, clinical management approaches, and future perspectives. Given the diverse clinical and genetic landscape of syndromic RP, the diagnosis may be challenging. However, an accurate and timely diagnosis is essential for optimal clinical management, prognostication, and potential treatment. Broadly, the syndromes associated with RP can be categorized into ciliopathies, inherited metabolic disorders, mitochondrial disorders, and miscellaneous syndromes. Among the ciliopathies associated with RP, Usher syndrome and Bardet-Biedl syndrome are the most well-known. Less common ciliopathies include Cohen syndrome, Joubert syndrome, cranioectodermal dysplasia, asphyxiating thoracic dystrophy, Mainzer-Saldino syndrome, and RHYNS syndrome. Several inherited metabolic disorders can present with RP including Zellweger spectrum disorders, adult Refsum disease, α-methylacyl-CoA racemase deficiency, certain mucopolysaccharidoses, ataxia with vitamin E deficiency, abetalipoproteinemia, several neuronal ceroid lipofuscinoses, mevalonic aciduria, PKAN/HARP syndrome, PHARC syndrome, and methylmalonic acidaemia with homocystinuria type cobalamin (cbl) C disease. Due to the mitochondria's essential role in supplying continuous energy to the retina, disruption of mitochondrial function can lead to RP, as seen in Kearns-Sayre syndrome, NARP syndrome, primary coenzyme Q10 deficiency, SSBP1-associated disease, and long chain 3-hydroxyacyl-CoA dehydrogenase deficiency. Lastly, Cockayne syndrome and PERCHING syndrome can present with RP, but they do not fit the abovementioned hierarchy and are thus categorized as 'Miscellaneous'. Several first-in-human clinical trials are underway or in preparation for some of these syndromic forms of RP.

An Autopsy Analysis of a Patient With Long-Chain 3-Hydroxyacyl-CoA Dehydrogenase Deficiency Caused by Compound Heterozygous HADHA Gene Mutations

ABSTRACT

Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency is a rare mitochondrial disease characterized by lipid oxidation disorder. It is an autosomal recessive disease induced by a mutation in the HADHA gene, which encodes the LCHAD deficiency. The clinical manifestations of this disease are diverse, primarily affecting the heart, liver, and skeletal muscles. Common symptoms include cardiomyopathy, peripheral neuropathy, retinopathy, and even lead to death in severe cases.Herein, we report a patient who was hospitalized due to flatulence, crying, irritability, and died of acute cardiopulmonary failure after 8 days in hospital. An autopsy was performed to determine the cause of death. Clinical examination revealed abnormal liver and kidney function, and the genetic metabolic disease profile indicated significantly elevated levels of long-chain acyl-carnitine and long-chain 3-OH-acyl-carnitine. Histopathological examination revealed diffuse hepatic steatosis, and the genetic sequencing results detected compound heterozygous mutations in the HADHA gene (c.1528G>C [p.E510Q] and c.703_704dupCG [p.T236Gfs*3]). Of note, the mother had a history of acute fatty liver during pregnancy. Collectively, our study may contribute to understanding the HADHA gene mutation profile and the clinical phenotype of LCHAD deficiency, emphasizing the importance of genetic testing in forensic pathology.

New Acylcarnitine Ratio as a Reliable Indicator of Long-Chain 3-Hydroxyacyl-CoA Dehydrogenase Deficiency

Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) and mitochondrial trifunctional protein (MTP) deficiencies are rare fatal disorders of fatty acid β-oxidation with no apparent genotype-phenotype correlation. The measurement of acylcarnitines by MS/MS is a current diagnostic workup in these disorders. Nevertheless, false-positive and false-negative results have been reported, highlighting a necessity for more sensitive and specific biomarkers. This study included 54 patients with LCHAD/MTP deficiency that has been confirmed by biochemical and molecular methods. The analysis of acylcarnitines in dried blood spots was performed using ESI-MS/MS. The established "HADHA ratio" = (C16OH + C18OH + C18:1OH)/C0 was significantly elevated in all 54 affected individuals in comparison to the control group. Apart from 54 LCHAD deficiency patients, the "HADHA ratio" was calculated in 19 patients with very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency. As VLCAD-deficient patients did not show increased "HADHA ratio", the results emphasized the high specificity of this new ratio. Therefore, the "HADHA ratio" was shown to be instrumental in improving the overall performance of MS/MS-based analysis of acylcarnitine levels in the diagnostics of LCHAD/MTP deficiencies. The ratio was demonstrated to increase the sensitivity and specificity of this method and reduce the chances of false-negative results.

A case report of necrotizing enterocolitis in a moderately preterm neonate with LCHADD-A call to focus on the basics while utilizing advanced new therapies

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) is an autosomal recessive condition of impaired beta-oxidation. Traditionally, treatment included restriction of dietary long-chain fatty acids via a low-fat diet and supplementation of medium chain triglycerides. In 2020, triheptanoin received FDA approval as an alternative source of medium chain fatty acids for individuals with long-chain fatty acid oxidation disorders (LC-FAOD). We present a case of a moderately preterm neonate born at 33 2/7 weeks gestational age with LCHADD who received triheptanoin and developed necrotizing enterocolitis (NEC). Prematurity is known as a major risk factor for NEC, with risk increasing with decreasing gestational age. To our knowledge, NEC has not previously been reported in patients with LCHADD or with triheptanoin use. While metabolic formula is part of the standard of care for LC-FAOD in early life, preterm neonates may benefit from more aggressive attempts to use skimmed human milk to minimize exposure to formula during the risk period for NEC during feed advancement. This risk period may be longer in neonates with LC-FAOD compared to otherwise healthy premature neonates.

A novel HADHA variant associated with an atypical moderate and late-onset LCHAD deficiency

Background

Long chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) is a rare inherited disease caused by pathogenic variants of HADHA gene. Along with signs common to fatty acid oxidation defects (FAOD), specific retina and heart alterations are observed. Because long-chain fatty acid oxidation is selectively affected, supplementations with short/medium-chain fats represent energetic sources bypassing the enzymatic blockade. Here, we report on an atypical presentation of the disease.

Methods

Clinical features were described with medical explorations including ophthalmic and cardiac examination. Biological underlying defects were investigated by measurements of biochemical metabolites and by fluxomic studies of mitochondrial β-oxidation. Whole exome sequencing and molecular validation of variants confirmed the diagnosis.

Results

The patient has developed at nine years an unlabeled maculopathy, and at 28 years, an acute cardiac decompensation without any premise. Blood individual acylcarnitine analysis showed a rise in hydroxylated long-chain fatty acids and fluxomic studies validated enzyme blockade consistent with LCHADD. Genetic analysis revealed the common p.(Glu510Gln) variant in HADHA, in trans with a novel variant c.1108G > A, p.(Gly370Arg) located in the NAD binding domain. Patient pathology was responsive to triheptanoin supplementation.

Conclusion

This atypical LCHADD form report should encourage the early assessment of biochemical and genetic testing as a specific management is recommended (combination with fast avoidance, low fat-high carbohydrate diet, medium-even-chain triglycerides or triheptanoin supplementation).

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Mild hyperpigmented macular dots could be the first and early symptom of moderate LCHAD.

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The novel HADHA c.1108G > A, p.(Gly370Arg) is hypomorphic and associated with moderate LCHAD.

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Atypical and late LCHAD can be deciphered by joint biochemical and genetical investigations.

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Acylcarnitines must be tested in unexplained macular dystrophy and/or dilated cardiomyopathy.

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Supplementation with the triglyceride triheptanoin is effective.

Evidence that Oxidative Disbalance and Mitochondrial Dysfunction are Involved in the Pathophysiology of Fatty Acid Oxidation Disorders

Mitochondrial fatty acid β-oxidation disorders (FAODs) are a group of about 20 diseases which are caused by specific mutations in genes that codify proteins or enzymes involved in the fatty acid transport and mitochondrial β-oxidation. As a consequence of these inherited metabolic defects, fatty acids can not be used as an appropriate energetic source during special conditions, such as prolonged fasting, exercise or other catabolic states. Therefore, patients usually present hepatopathy, cardiomyopathy, severe skeletal myopathy and neuropathy, besides biochemical features like hypoketotic hypoglycemia, metabolic acidosis, hypotony and hyperammonemia. This set of symptoms seems to be related not only with the energy deficiency, but also with toxic effects provoked by fatty acids and carnitine derivatives accumulated in the tissues of the patients. The understanding of the mechanisms by which these metabolites provoke tissue injury in FAODs is crucial for the developmental of novel therapeutic strategies that promote increased life expectancy, as well as improved life quality for patients. In this sense, the objective of this review is to present evidence from the scientific literature on the role of oxidative damage and mitochondrial dysfunction in the pathogenesis of the most prevalent FAODs: medium-chain acyl-CoA dehydrogenase (MCAD), long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) and very long-chain acyl-CoA dehydrogenase (VLCAD) deficiencies. It is expected that the findings presented in this review, obtained from both animal model and patients studies, may contribute to a better comprehension of the pathophysiology of these diseases.

Analysis of a family with mitochondrial trifunctional protein deficiency caused by HADHA gene mutations

Mitochondrial trifunctional protein (MTP) deficiency (MTPD; MIM 609015) is a metabolic disease of fatty acid oxidation. MTPD is an autosomal recessive disorder caused by mutations in the HADHA gene, encoding the α-subunit of a trifunctional protease, or in the HADHB gene, encoding the β-subunit of a trifunctional protease. To the best of our knowledge, only two cases of families with MTPD due to HADHB gene mutations have been reported in China, and the HADHA gene mutation has not been reported in a Chinese family with MTPD. The present study reported the clinical characteristics and compound heterozygous HADHA gene mutations of two patients with MTPD in the Chinese population. The medical history, routine examination data, blood acyl-carnitine analysis results, results of pathological examination after autopsy and family pedigree map were collected for patients with MTPD. The HADHA gene was analyzed by Sanger sequencing or high-throughput sequencing, the pathogenicity of the newly discovered variant was interpreted by bioinformatics analysis, and the function of the mutated protein was modeled and analyzed according to 3D structure. The two patients with MTPD experienced metabolic crises and died following an infectious disease. Lactate dehydrogenase, creatine kinase (CK), CK-MB and liver enzyme abnormalities were observed in routine examinations. Tandem mass spectrometry revealed that long-chain acyl-carnitine was markedly elevated in blood samples from the patients with MTPD. The autopsy results for one child revealed fat accumulation in the liver and heart. Next-generation sequencing detected compound heterozygous c.703C>T (p.R235W) and c.2107G>A (p.G703R) mutations in the HADHA gene. The mother did not have acute fatty liver during pregnancy with the two patients. Using amniotic fluid prenatal diagnostic testing, the unborn child was confirmed to carry only c.2107G>A (p.G703R). Molecular mechanistic analysis indicated that the two variants affected the conformation of the α-subunit of the MTP enzyme complex, and consequently affected the stability and function of the enzyme complex. The present study comprehensively analyzed the cases, including exome sequencing and protein structure analysis and, to the best of our knowledge, describes the first observation of compound heterozygous mutations in the HADHA gene underlying this disorder in China. The clinical phenotypes of the two heterozygous variants of the HADHA gene are non-lethal. The present study may improve understanding of the HADHA gene mutation spectrum and clinical phenotype in the Chinese population.

Retinitis pigmentosa as a clinical presentation of LCHAD deficiency: A clinical case and review of the literature

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency is a rare metabolic disease caused by a specific mutation in the HADHA gene, which leads to an alteration in the metabolic pathway of fatty acids. Its most frequent form of presentation at the ophthalmological level is retinitis pigmentosa, and in some cases the ophthalmologist could be the first one to alert the other paediatric specialties to carry out a multidisciplinary approach to the case. The case is presented of a patient with long-chain 3-hydroxyacyl-CoA dehydrogenase deficit detected in neonatal screening, and which clinically debuted as pigmentary retinosis with no alteration in visual acuity as observed in the fundus images and optical coherence tomography of the retina provided. Finally, a review of the literature of this potentially lethal pathology is presented, and the main pathological and clinical features are highlighted.

The spectrum of peripheral neuropathy in disorders of the mitochondrial trifunctional protein

Peripheral neuropathy is a known irreversible long-term complication of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) and mitochondrial trifunctional protein deficiency (MTPD), two inherited disorders of mitochondrial long-chain fatty acid oxidation. The underlying pathophysiology of neuropathy is still not fully understood. We report electrophysiological studies and neurological findings in a series of 8 LCHAD-deficient and 11 MTP-deficient patients. The median age at time of the study was 8.0 years (0.5-25 years). The overall prevalence of neuropathy was 58% with neuropathic symptoms being slightly more common in MTPD compared to LCHADD (70% vs 50%, respectively). Onset of neuropathy was significantly earlier in MTPD patients compared to LCHADD patients (median age at onset 4.7 vs 15.3 years, respectively, P = .047). In four patients, isolated peripheral neuropathy was the first and only presenting symptom, and in all four the diagnosis was missed by newborn screening. About half of the patients (45.5%) had a sensorimotor neuropathy, while 27.3% showed a pure motor form and another 27.3% an isolated sensory form. Despite early diagnosis by newborn screening and early initiation of therapy, peripheral neuropathy cannot be prevented in all patients with LCHADD/MTPD and has severe impact on the life of affected patients. Electrophysiology classifies LCHADD/MTPD neuropathy as axonal with secondary demyelination. A novel observation is that in patients with acute, fulminant onset of neuropathy, symptoms can be partly reversible. Further studies are needed to elucidate the underlying pathophysiology of axonal damage and possible therapeutic targets.

[New Inborn Errors of Metabolism added in the French program of neonatal screening]

Inborn Errors of Metabolism (IEM) are rare and heterogenous disorders. For most IEMs, clinical signs are non-specific or belated. Late diagnosis is frequent, leading to death or severe sequelae. Some IEM induce intermediate metabolites circulating in the blood. They may be detected by tandem mass spectrometry. This method allows the simultaneous detection of many IEM in different metabolic pathways. In France, newborn screening (NBS) program for IEM, limited to phenylketonuria for decades, has been recently extended to medium chain acyl-CoA dehydrogenase deficiency. Rationale, methodology and organization of this new NBS program are described. Seven other IEM (maple syrup urine disease, homocystinuria, tyrosinemia type I, glutaric aciduria type I, isovaleric acidemia, long chain hydroxy-acyl-CoA dehydrogenase deficiency, carnitine uptake disorder) should be screened in the next program extension. Efforts are needed to fully understand the predictive value of each abnormal testing at birth, decrease the false positive rate, and develop the adequate management strategies.

Long-term experience with triheptanoin in 12 Austrian patients with long-chain fatty acid oxidation disorders

Background

Long-chain fatty acid oxidation disorders (LC-FAOD) are a group of rare inborn errors of metabolism with autosomal recessive inheritance that may cause life-threatening events. Treatment with triheptanoin, a synthetic seven-carbon fatty acid triglyceride compound with an anaplerotic effect, seems beneficial, but clinical experience is limited. We report our long-term experience in an Austrian cohort of LC-FAOD patients.

Methods

We retrospectively assessed clinical outcome and total hospitalization days per year before and after start with triheptanoin by reviewing medical records of 12 Austrian LC-FAOD patients

Results

For 12 Austrian LC-FAOD patients at three metabolic centers, triheptanoin was started shortly after birth in 3/12, and between 7.34 and 353.3 (median 44.5; mean 81.1) months of age in 9/12 patients. For 11 pediatric patients, mean duration of triheptanoin intake was 5.3 (median 3.9, range 1.2–15.7) years, 10/11 pediatric patients have an ongoing intake of triheptanoin. One patient quit therapy due to reported side effects. Total hospitalization days per year compared to before triheptanoin treatment decreased by 82.3% from 27.1 (range 11–65) days per year to 4.8 (range 0–13) days per year, and hospitalization days in the one year pre- compared to the one year post-triheptanoin decreased by 69.8% from 27.1 (range 4–75) days to 8.2 (range 0–25) days. All patients are in good clinical condition, show normal psychomotor development and no impairment in daily life activities.

Conclusion

In this retrospective observational study in an Austrian LC-FAOD cohort, triheptanoin data show improvement in disease course. Triheptanoin appears to be a safe and beneficial treatment option in LC-FAOD. For further clarification, additional prospective randomized controlled trials are needed.

Liver failure in pregnancy: a review of 25 cases

We retrospectively reviewed the medical records from 25 pregnant women with liver failure from May 2009 to July 2019. Data describing clinical symptoms and manifestations, routine blood analyses, coagulation, and liver and kidney function were extracted. Swansea criteria were assessed to identify variables with prognostic significance for maternal mortality. The results showed that acute fatty liver was the primary cause of liver failure and 8 (88.89%) patients died within 7 days. Swansea diagnostic criteria for assessing the severity of liver failure were consistent with Chinese guidelines and were more systematic and convenient. The incidence of postpartum haemorrhage was 76%, and the velocity of bleeding was approximately 600 mL per hour. Increased Swansea score, hepatic encephalopathy and decreased PWR were important prognostic indicators for mortality. Recovery during the 7 days postpartum period was an important determinant of maternal outcomes.Impact statementWhat is already known on this subject? Liver failure in pregnant women is a rare but potentially devastating disease with a high rate of short-term morbidity and mortality. There are limited reports about clinical predictors of maternal-foetal outcomes and the dilemmas faced in the term of delivery.What the results of this study add? The incidence of postpartum haemorrhage was 76% in pregnant women with liver failure, but the velocity of bleeding was approximately 600 mL per hour. Our study revealed the Swansea score and the ratio of hepatic encephalopathy were significantly higher and platelet-to-white blood cell ratio (PWR) was lower in women who died compared to those who survived. During treatment period, 8 (88.89%) patients died within 7 days.What the implications are of these findings for clinical practice and/or further research? Swansea score, hepatic encephalopathy and PWR were important prognostic indicators for mortality in pregnant women with liver failure. Recovery during the 7 days postpartum period was an important determinant of maternal outcomes. Our findings may prompt researchers to conduct a large multicentre study to evaluate the prognostic indicators for mortality in pregnant women with liver failure.

Recent Advances in the Pathophysiology of Fatty Acid Oxidation Defects: Secondary Alterations of Bioenergetics and Mitochondrial Calcium Homeostasis Caused by the Accumulating Fatty Acids

Deficiencies of medium-chain acyl-CoA dehydrogenase, mitochondrial trifunctional protein, isolated long-chain 3-hydroxyacyl-CoA dehydrogenase, and very long-chain acyl-CoA dehydrogenase activities are considered the most frequent fatty acid oxidation defects (FAOD). They are biochemically characterized by the accumulation of medium-chain, long-chain hydroxyl, and long-chain fatty acids and derivatives, respectively, in tissues and biological fluids of the affected patients. Clinical manifestations commonly include hypoglycemia, cardiomyopathy, and recurrent rhabdomyolysis. Although the pathogenesis of these diseases is still poorly understood, energy deprivation secondary to blockage of fatty acid degradation seems to play an important role. However, recent evidence indicates that the predominant fatty acids accumulating in these disorders disrupt mitochondrial functions and are involved in their pathophysiology, possibly explaining the lactic acidosis, mitochondrial morphological alterations, and altered mitochondrial biochemical parameters found in tissues and cultured fibroblasts from some affected patients and also in animal models of these diseases. In this review, we will update the present knowledge on disturbances of mitochondrial bioenergetics, calcium homeostasis, uncoupling of oxidative phosphorylation, and mitochondrial permeability transition induction provoked by the major fatty acids accumulating in prevalent FAOD. It is emphasized that further in vivo studies carried out in tissues from affected patients and from animal genetic models of these disorders are necessary to confirm the present evidence mostly achieved from in vitro experiments.

Retinitis pigmentosa as a clinical presentation of LCHAD deficiency: A clinical case and review of the literature

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency is a rare metabolic disease caused by a specific mutation in the HADHA gene, which leads to an alteration in the metabolic pathway of fatty acids. Its most frequent form of presentation at the ophthalmological level is retinitis pigmentosa, and in some cases the ophthalmologist could be the first one to alert the other paediatric specialties to carry out a multidisciplinary approach to the case. The case is presented of a patient with long-chain 3-hydroxyacyl-CoA dehydrogenase deficit detected in neonatal screening, and which clinically debuted as pigmentary retinosis with no alteration in visual acuity as observed in the fundus images and optical coherence tomography of the retina provided. Finally, a review of the literature of this potentially lethal pathology is presented, and the main pathological and clinical features are highlighted.

HADHA and HADHB gene associated phenotypes - Identification of rare variants in a patient cohort by Next Generation Sequencing

The heterooctameric mitochondrial trifunctional protein (MTP), composed of four α- and β-subunits harbours three enzymes that each perform a different function in mitochondrial fatty acid β-oxidation. Pathogenic variants in the MTP genes (HADHA and HADHB) cause MTP deficiency, a rare autosomal recessive metabolic disorder characterized by phenotypic heterogeneity ranging from severe, early-onset, cardiac disease to milder, later-onset, myopathy and neuropathy. Since metabolic myopathies and neuropathies are a group of rare genetic disorders and their associated muscle symptoms may be subtle, the diagnosis is often delayed. Here we evaluated data of 161 patients with myopathy and 242 patients with neuropathy via next generation sequencing (NGS) and report the diagnostic yield in three patients of this cohort by the detection of disease-causing variants in the HADHA or HADHB gene. The mitigated phenotypes of this treatable disease were missed by the newborn screening, highlighting the importance of phenotype-based NGS analysis in patients with rare and clinically very variable disorders such as MTP deficiency.